Method and arrangement for controlling feed in rock drilling

ABSTRACT

A method and an arrangement for controlling the feed of a rock drill. In the method, the pressure in a pressure conduit ( 7   a ) of a pressure-fluid-operated feed motor ( 6 ) is measured, and when the pressure value measured is below the pre-set threshold value, the volume flow of the pressure fluid delivered to the feed motor and thereby the feed rate of the feed motor ( 6 ) are adjusted, and when the pressure value measured is above the pre-set threshold value, the feed is adjusted by adjusting the pressure of the pressure fluid delivered to the feed motor ( 6 ). In the arrangement, a pressure detector ( 13 ) is arranged in the pressure conduit ( 7   a ) of the feed motor ( 6 ). The detector is arranged to control the feed of the pressure fluid delivered to the feed motor ( 6 ) in such a way that when the pressure is below the pre-set threshold value, the feed is controlled by adjusting the volume flow of the pressure fluid and, correspondingly, when the pressure value is above the pre-set threshold value, the pressure detector adjusts the feed of the pressure fluid according to the pressure of the pressure fluid.

BACKGROUND OF THE INVENTION

The invention relates to a method for controlling the feed of apressure-fluid-operated rock drilling apparatus when a rock drill is fedforward by a pressure-fluid-operated feed motor.

The invention further relates to an arrangement for controlling the feedof a pressure-fluid-operated rock drilling apparatus comprising a rockdrill, a feed beam along which the rock drill moves, apressure-fluid-operated feed motor for moving the rock drill along thefeed beam, control means for adjusting the feed of the rock drill, andmeans for adjusting the flow of the pressure fluid and thereby the feedrate of the feed motor.

The aim in rock drilling is on the one hand to control the entiredrilling operation such that ineffective time can be minimized and onthe other hand to conduct the actual drilling operation such that a holecan be drilled as close to the desired position as possible, while theapparatus is subjected to as little wear and damage as possible. Inpractice, the impact and rotation parameters and the feed of the rockdrill in today's rock drilling apparatus can be adjusted by differentcontrols. In practice, solutions widely used are the ones in which thedrilling power is adjusted and an automatic control adjusts both impactand feed pressure in accordance with pre-set control parameters. Becausethe rock to be drilled and the drilling situations vary, there usuallyalso exists a separate manual feed control system by which the feedpressure can be deflected from the pressure defined by the parameters,so that the drilling operation can also be adjusted in accordance withthe conditions. In connection with collaring, or before the actualdrilling is started, it is, however, difficult to adjust the drillingoperation by adjusting the pressure of the feed, since the feed pressuredoes not take into account, for example, the effect of an inclinedsurface on the motion of the drill bit and on the bending of the drillrod, and the drilling step is therefore not very easy to adjust atpresent. The position of the feed apparatus and various friction factorsin the feed apparatus as such make it impossible to accurately controlthe collaring step and the moving of the drill bit to the rock surfacewith one and the same pressure value.

SUMMARY OF THE INVENTION

The object of the present invention is to provide such a method andarrangement for controlling the feed in rock drilling that the rockdrilling operation can be better adjusted, if desired, in the collaringstep and also during the actual drilling under exceptional conditions.

The method of the invention is characterized in that at least in thecollaring step the pressure of the pressure fluid in a pressure conduitof the feed motor is measured, that when the pressure of the pressurefluid is below a pre-set threshold value, the volume flow of thepressure fluid delivered to the feed motor is adjusted so as to adjustthe feed rate, and that when the pressure of the pressure fluid is abovesaid pre-set threshold value, the feed is controlled by adjusting thepressure of the pressure fluid delivered to the feed motor.

The arrangement of the invention is characterized in that thearrangement comprises a pressure detector that is arranged to detect thepressure of the pressure fluid in the pressure conduit of the feedmotor; and that the pressure detector is arranged to control the controlmeans in such a way that when the pressure in the pressure conduit ofthe feed motor is below a pre-set threshold value at least in thecollaring step, the control means are arranged to adjust the volume flowof the pressure fluid and thereby the feed rate of the feed motor, andthat when the pressure in the pressure conduit of the feed motor isabove the value pre-set for the pressure detector, the control means arearranged to control the pressure of the pressure fluid in the pressureconduit of the feed motor.

The essential idea of the invention is that when the drill bit is movedtoward the rock in the collaring step, the feed rate at which the drillbit moves toward the rock is adjusted. If, for example, the surface isinclined, the feed rate at the beginning of the drilling operation canbe adjusted to be low, so that the collaring will not bend nor inclinethe drill apparatus, which is what would happen if the feed pressurewere adjusted. Another essential idea of the invention is that when aproper rock contact has been established so that there is no risk ofbending or inclining, the feed control automatically switches to normalfeed pressure, and from then on the drilling operation is conductedunder the control of normal drilling parameters.

The advantage of the invention is that the rock contact can beestablished and the collaring conducted accurately and carefully byadjusting of feed rate, whereby the drilling is simple and easy for theuser to control. Correspondingly, if the drill bit is in firm contactwith the rock to be drilled, normal drilling, where the adjustment isbased on the adjustment of pressure, is safe to use. In this way, thedrilling control is comfortable and operatively logical for the user tocontrol. The method of the invention helps to avoid mispositioning ofdrill holes, and faults in the machinery, and simultaneously makes theapparatus easier to use.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail in th) attacheddrawings, in which

FIG. 1 is a schematic view of an embodiment of an arrangement accordingto the invention in a rock drilling apparatus, and

FIG. 2 is a schematic view of rate and pressure curves during drilling,obtained by using the arrangement according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a schematic view of an embodiment of an arrangement accordingto the invention in a rock drilling apparatus. The arrangement comprisesa rock drill 1 to which is connected a drill rod 2 and a drill bit 3 atthe end of the drill rod 2. The rock drill 1 is arranged to move along afeed beam 4 in the longitudinal direction toward the front end of thefeed beam 4 during the drilling. In the collaring step, the feed beam 4is first moved toward rock 5, after which the rock drill 1 is movedforward.

The rock drill 1 is nowadays usually operated hydraulically: pressurefluid is supplied to the rock drill through pressure fluid conduits or,usually, hoses. For the sake of clarity, only pressure conduits 7 a and7 b connected to a feed motor 6 are shown in the figure. The pressurefluid is delivered through conduit 7 a to the feed motor so as to movethe rock drill 1 in the drilling direction, and the returning pressurefluid is discharged through conduit 7 b. The return motion is effectednormally by cross-connecting the conduits. As regards the operation, thefeed of the pressure fluid is controlled by control means, which includea separate control unit 8 adjusting the amount of pressure fluid indifferent hoses and, correspondingly, the pressure in each hose inaccordance with pre-set manually adjusted parameters. The pressure fluidis supplied in a manner known per se by a pressure fluid pump 9, and thepressure fluid will return to a pressure fluid container 10. The pumpand the container are commonly known, so they will not be described ingreater detail herein.

The figure shows a schematic view of a feed motor 6, indicated by asymbol, which is a hydraulic motor or a hydraulic cylinder. Both ahydraulic motor and a hydraulic cylinder operate as a feed motor that isarranged in a manner known per se to move the rock drill 1 in bothdirections lengthwise of the feed beam 4. The transfer mechanisms andconnections are commonly known per se, and so they will not be describedin greater detail herein. Pressure fluid conduit 7 a is arranged tosupply fluid to the feed motor 6, i.e. a pressure fluid hose is arrangedto be controlled such that the feed of the pressure fluid is controlledby a feed adjustment valve 11. The volume flow of the pressure fluidflowing through the adjustment valve is dependent on the position of amanual feed control 12. The feed rate can be given a certain commonlyused nominal value, which can be raised or reduced by means of the feedcontrol 12 according to the need. Further, a pressure detector 13 isconnected to pressure fluid conduit 7 a of the feed motor, the detectordetecting when the drill bit 3 hits the rock, so that the feedresistance increases. At a suitable feed rate, the drill bit can machinethe rock gradually, for example, in an inclined rock surface withoutthat the feed pressure exceeds the set value of the pressure detector13. The low feed rate can be employed until an essentially full-sizedrill surface has been achieved for the drill bit, after which thepressure continues to rise. As the pressure detector 13 detects that thethreshold pressure has been exceeded, the feed control 12 begins tocontrol the feed pressure in pressure fluid conduit 7 a through the feedcontrol valve 11. The feed pressure then settles at the level defined bythe parameters of the control unit 8, and it can be deflected from thatlevel in either direction by the feed control 12. In practice, as thepressure detector 13 detects that a proper rock contact has beenestablished, the drilling operation, controlled by the control unit 8,switches to normal sequence drilling operation, and the drilling stepsare then automatically conducted in the desired manner.

If, for some reason, the material being drilled comprises broken rock orhollow spaces, the feed pressure easily drops below the threshold valueof the pressure detector 13. The pressure detector 13 can then make theapparatus control the feed rate rather than the feed pressure byswitching the feed control 12 to control the volume flow of the feedcontrol valve 11 rather than the pressure. Correspondingly, when thepoint causing little resistance has been passed and the drill bit 3 hashit the hard surface, the pressure detector 13 re-switches the feed tooperate in accordance with the pressure.

FIG. 2 shows a schematic view of how the feed pressure and feed rate ofan embodiment of a rock drilling apparatus according to FIG. 1 vary indifferent drilling situations. Curve V in the figure indicates the feedrate, and curve P indicates the pressure of the pressure fluid in thefeed motor.

At point A on the left in the figure, the feed beam is in the collaringposition. Up to point P on the right, curve V indicates how the rate ofthe feed motor remains constant, whereas the feed pressure variesslightly, since the friction factors, etc. change the feed resistance ofthe feed motor. At point B the user slows down the feed rate, whichdrops but remains essentially constant after the slow-down up to pointC, while the feed pressure continues to vary to some extent. At point Cthe drill bit comes into contact with the rock surface and the feedpressure begins to rise, while the feed rate remains essentially thesame. At point D the feed pressure value exceeds the pre-set thresholdvalue of the pressure detector 13, and the feed pressure settles at asuitable pressure level for the actual collaring, remaining essentiallyconstant at that level, while the feed rate begins to vary. In this stepat the latest, the impact operation of the rock drill is switched on,although in principle it can have been operative all the time from pointA onward. At point E the collaring step is over, and the feed pressurebegins to rise in a predefined manner, and the feed rate will vary withthe drilling resistance. The feed pressure, in turn, controls the impactand rotation operations of the rock drill in a suitable manner known perse.

As the drill hits softer or broken rock or a hollow space, the feedpressure drops suddenly at point F, and as it drops below the pre-setthreshold value of the pressure detector 13, the pressure detectorbegins to control the drilling by adjusting the feed rate rather thanthe pressure. From point F to point G, the feed rate thus remainsessentially constant, and the feed pressure varies with the conditions.At point G the feed pressure starts to rise again because the rockmaterial is firmer and harder, and at point H the pressure exceeds thepre-set threshold value of the pressure detector 13, after which thedrilling control begins to operate on the basis of the feed pressure inthe manner described above, while the feed rate starts to vary.

In the above description and the drawings, the invention is described byway of an example, and it is not to be construed as being limited bythem. The essential feature is that the drilling control is implementedby controlling the feed as the drill moves toward the rock and, ifnecessary, by adjusting the feed rate under conditions where there islittle feed resistance, and during the actual drilling the same feedcontrol is switched to control the feed pressure instead of the feedrate. The other drilling steps can be implemented in differentpreviously known ways and by different sequence drillings in accordancewith pre-set definitions.

What is claimed is:
 1. A method of controlling a rock drilling apparatusthat includes a rock drill, a pressure-fluid operated feed motor forfeeding the rock drill forward, and a pressure conduit for supplyingpressure fluid to the feed motor, said method comprising, during acollaring step: supplying pressure fluid to the feed motor via thepressure conduit, comparing the pressure of the pressure fluid in thepressure conduit with a pre-set threshold value, when the pressure ofthe pressure fluid in the pressure conduit is below the pre-setthreshold value, controlling the feed rate by adjusting the volume flowof pressure fluid delivered to the motor, and when the pressure of thepressure fluid in the pressure conduit is above the pre-set thresholdvalue, controlling the feed rate by adjusting the pressure of pressurefluid delivered to the motor.
 2. A method according to claim 1,comprising continuing to compare the pressure of the pressure fluid inthe pressure conduit with the pre-set threshold value during drillingand, in the event that the pressure of the pressure fluid in thepressure conduit falls below the pre-set threshold value, adjusting thevolume flow of pressure fluid to control the feed rate, and when thepressure of the pressure fluid in the pressure conduit increases oncemore above the pre-set threshold value, adjusting the pressure of thepressure fluid to control the feed rate.
 3. A method of controlling arock drilling apparatus that includes a rock drill, a pressure-fluidoperated feed motor for feeding the rock drill forward, and a pressureconduit for supplying pressure fluid to the feed motor, said methodcomprising: supplying pressure fluid to the feed motor via the pressureconduit, comparing the pressure of the pressure fluid in the pressureconduit with a pre-set threshold value, when the pressure of thepressure fluid in the pressure conduit is below the threshold value,controlling the feed rate by adjusting the volume flow of pressure fluiddelivered to the motor, and when the pressure of the pressure fluid inthe pressure conduit is above the threshold value, controlling the feedrate by adjusting the pressure of pressure fluid delivered to the motor.4. A rock drill apparatus including: a rock drill, a feed beam on whichthe rock drill is mounted for feeding movement, a pressure-fluidoperated feed motor for moving the rock drill along the feed beam, apressure conduit for feeding pressure fluid to the feed motor, apressure detector for detecting the pressure of pressure fluid in thepressure conduit, and a control means responsive to the pressuredetector for controlling supply of the pressure fluid to the feed motorin a manner such that when the pressure of the pressure fluid in thepressure conduit is below a preset threshold value, the control meanscontrols the feed rate by adjusting the volume flow of pressure fluiddelivered to the motor, and when the pressure of the pressure fluid inthe pressure conduit is above the pre-set threshold value, the controlmeans controls the feed rate by adjusting the pressure of pressure fluiddelivered to the motor.
 5. A rock drill apparatus according to claim 4,comprising a manual control for controlling supply of the pressure fluidto the feed motor.